PMID:6454
| Citation |
Prusiner, S, Davis, JN and Stadtman, ER (1976) Regulation of glutaminase B in Escherichia coli. I. Purification, properties, and cold lability. J. Biol. Chem. 251:3447-56 |
|---|---|
| Abstract |
Escherichia coli contains two glutaminases, A and B, with pH optima below pH 5 and above pH 7, respectively. Neither glutaminase A nor B is released from E. coli by osmotic shock. Glutaminase B has been purified 6,000-fold and the purified preparation is estimated to contain about 40% glutaminase B. The enzyme has a molecular weight of 90,000 and an isoelectric point of 5.4. Glutaminase B exhibits a broad pH optimum between 7.1 and 9.0. Only L-glutamine is deamidated by glutaminase B, L-asparagine and D-glutamine are not deamidated. The substrate saturation curve for glutaminase B shows an intermediary plateau region. Like many regulatory enzymes, glutaminase B is cold-labile. The enzyme is inactivated by cooling and activated by warming; both processes are first order with respect to time. The activation energy for activation by warming was calculated to be 5900 cal/mol. Activation by warming increased the Vmax and decreased the S0.5 for L-glutamine, but did not alter the molecular weight of the catalytically active enzyme. Borate and glutamate protected glutaminase B from inactivation by cold. |
| Links | |
| Keywords |
Cold Temperature; Drug Stability; Escherichia coli/enzymology; Glutaminase/isolation & purification; Glutaminase/metabolism; Hydrogen-Ion Concentration; Isoenzymes/isolation & purification; Isoenzymes/metabolism; Kinetics; Molecular Weight; Temperature; Thermodynamics; Time Factors |
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